Wireless communication systems typically employ one or more modulation scheme to communicate voice, data and control information between the base station and a mobile terminal. In the wireless communication systems employing multiple modulation schemes, the mobile terminal must be either informed of the modulation type in advance or should detect it from the received data. Informing the mobile terminal the modulation type for each burst before the transmission of the information requires sending extra information conveying the modulation types from the transmitter to the receiver and it requires extra bandwidth.
In addition, the mobile terminals are required to be small and low cost. The receiver architecture based on direct conversion can fulfill the cost and size requirements, because the direct conversion receiver can eliminate components, such as image rejection filter and IF (Intermediate Frequency) mixer. However, a direct conversion receiver suffers from DC offset problems, which can cause the receiver to lose connection and drop calls.
Direct current (DC) offset in receivers presents a major problem for receiver performance. The most popular idea for reducing the DC offset is do long-term averaging of the baseband signal and removing the DC by subtracting the DC estimate. However, in the EDGE systems, DC offsets are different for different frequencies due to the frequency hopping performed as part of the standard. Therefore long-term averaging is not possible in EDGE systems. Further, the training sequences in EDGE do not have zero mean and short-term averaging over only one EDGE burst (≈140-150 data samples) which gives rise to residual DC offset that can degrade the receiver performance.
Thus, a need still remains for wireless communication system with signal processing mechanism to identify the modulation scheme, estimate the communication channel, and resolve DC offset problems in the receiver. In view of the ever-increasing commercial competitive pressures, along with growing consumer expectations and the diminishing opportunities for meaningful product differentiation in the marketplace, it is increasingly critical that answers be found to these problems. Additionally, the need to reduce costs, improve efficiencies and performance, and meet competitive pressures adds an even greater urgency to the critical necessity for finding answers to these problems.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.